CMOS Voltage References: An Analytical and Practical Perspective

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Sub-1V Voltage Reference Circuit

The trend in integrated circuit fabrication since its inception has been a move towards decreasing geometry size to increase circuit capacity, speed, and to reduce power consumption. As transistor size decreases, the circuit functionality of a given area of substrate increases. Smaller device size also yields lower parasitic capacitance which increases speed and decreases power consumption. At the same time, operating voltage must also be scaled down due to the increased electric field and reduced breakdown voltage caused by the higher doping profile required by small device. Decreased operating voltage facilitates low power consumption which is increasingly important as circuit complexity increases. However, the voltage reference circuit becomes more difficult to design with low supply voltage.

The low operating voltage imposes two design constraints onto the voltage reference circuit. The first constraint is the output of the voltage reference circuit. The output voltage of the voltage reference circuit has to be lower than the supply voltage. The output voltage of most of the conventional bandgap voltage reference circuits discussed in Chapters 3 and 5 is 1.23 V. When the supply voltage is lowered to below 1 V, one wonders how to achieve a reference voltage with magnitude below 1 V. The voltage reference circuit capable of generating a lower output voltage is referred as sub-1V voltage reference circuit, which literally means the output of ...